We demonstrate adiabatically tapered fibers terminating in sub-micron tips that are clad with a higher-index material for coupling to an on-chip waveguide. This cladding enables coupling to a high-index waveguide without losing light to the buried oxide. A technique to clad the tip of the tapered fiber with a higher-index polymer is introduced. Conventional tapered waveguides and forked tapered waveguide structures are investigated for coupling from the clad fiber to the on-chip waveguide. We find the forked waveguide facilitates alignment and packaging, while the conventional taper leads to higher bandwidth. The insertion loss from a fiber through a forked coupler to a sub-micron silicon nitride waveguide is 1.1 dB and the 3 dB bandwidth is 90 nm. The coupling loss in the packaged device is 1.3 dB. With a fiber coupled to a conventional tapered waveguide, the loss is 1.4 dB with a 3 dB bandwidth extending beyond the range of the measurement apparatus, estimated to exceed 250 nm.

中文翻译：

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使用带帽绝热锥形光纤的低损耗，高带宽光纤到芯片耦合

我们展示了绝热的渐缩纤维，终止于亚微米级尖端，该尖端包覆有折射率较高的材料，可耦合至片上波导。该包层使得能够耦合至高折射率波导，而不会将光损失到掩埋氧化物。介绍了一种使用高折射率聚合物包覆锥形纤维尖端的技术。为了从包层光纤耦合到芯片上波导，研究了常规的锥形波导和叉形锥形波导结构。我们发现，叉形波导有助于对准和封装，而常规的锥度会导致更高的带宽。从光纤通过叉形耦合器到亚微米氮化硅波导的插入损耗为1.1 dB，3 dB带宽为90 nm。封装设备中的耦合损耗为1.3 dB。